This invention relates to apparatus and processes for sensing pressure changes within transformer fluids caused by internal faults. Upon the occurrence of an internally generated transformer fault, a relay can be energized for disconnecting the transformer from the power source to protect the transformer from excessive damage.
Transformers of the type enclosed in a dielectric fluid are subject to damage arising from faults occurring internally within the transformer and causing the transformer fluid to increase in both pressure and temperature. If the transformer is allowed to continue to operate under the fault conditions, the transformer becomes destroyed. Since the transformer internal gas and liquid pressure increases in relation to the amount of energy generated by the internal fault, means are currently available to sense the pressure increase and to operate a relay to remove electrical power from the transformer.
Other conditions which cause the transformer fluid pressure to increase are faults which occur outside the transformer (through faults) and pressure which is generated by seismic or other mechanical disturbances to the transformer fluid. Mechanical type sensing and control devices are currently employed to sense the pressure increase within the transformer fluid and to energize a relay to electrically disconnect the transformer from the power source before catastrophic damage occurs. Mechanical type pressure sensing means and relay assemblages are unable to accurately differentiate between internal faults and through faults. Attempts to increase the sensitivity of the mechanical type pressure sensing elements to internal fault detection quite often cause the transformer to become disconnected from the line when pressure increases are of a temporary nondestructive type through fault. Attempts to over-compensate the mechanical sensing element to allow temporary through fault pressure increases to occur without tripping can also allow internal faults to escape detection which can be destructive to the transformer.
The purpose of this invention is to provide a programmable fault detecting relay for transformers which can differentiate between pressure increases caused by temporary through faults and mechanical disturbances. The fault detecting relay of this invention therefore is able to operate signal and relay equipment for disconnecting the transformer from the line when internal faults occur and to allow the transformer to remain connected to the line for the duration of pressure increases caused by temporary through faults and mechanical disturbances.